The present invention relates generally to ring laser gyros (RLGs). In particular, the invention is a system for enhancing path length control (PLC) operation in RLGs.
Ring laser gyros (RLGs) are instruments used to measure angular rotation. They include a cavity in which two laser beams travel in counter-rotating (i.e., opposite) directions. The laser beams create an optical interference pattern having characteristics representative of the amount by which the RLG is rotated. The interference pattern is detected and processed to provide the angular rotation measurements. Instruments of this type are generally known and disclosed, for example, in the following U.S. Patents:
RLGs are subject to a phenomenon known as xe2x80x9clock-inxe2x80x9d which can degrade their measurement accuracy. One known approach for minimizing lock-in is dithering. Dithering is the mechanical oscillation of the RLG. This function is provided by a dither system which includes a motor for generating the oscillations, and a transducer for generating a signal known as the dither pick-off which is representative of the dither motion amplitude and frequency. The dither frequency is typically in the range of 600 Hz. The dither pick-off signal is processed along with the detected interference pattern to provide the angular rotation measurements
RLGs also typically include a path length control (PLC) system which adjusts the path length of the laser beams within the RLG cavity to maintain peak steady state intensity/power. This function is provided by one or more transducer mirrors which are driven by a control system. A primary input to the control system is the laser intensity monitor signal (LIM signal) generated as a function of one of the laser beams. In addition to a DC component (which is filtered out and not used for the PLC function), the LIM signal includes an AC component at twice the dither frequency (each turnaround) known as the single beam signal (SBS) and 3 KHz modulation information. The SBS is a sinusoidal variation component which occurs at points in time corresponding to the mechanical turnaround points of the dither periods. The AC components (SBS and 3 KHz modulation) of the LIM signal are amplified and inputted into a demodulator along with demodulator clock gating signals (a pair of complimentary 3 KHz square wave signals in one embodiment). The demodulated AC components of the LIM signal are then integrated to produce the transducer mirror drive signal.
There remains a continuing need for RLGs with improved measurement accuracy. Systems that provide significant performance enhancements and can be efficiently implemented with relatively little hardware and software overhead would be especially desirable.
The present invention is a single beam signal (SBS) blanking system implemented in the path length control (PLC) system of a ring laser gyro. The system enhances the PLC""s ability to maintain peak power operation, and thereby increases measurement accuracy performance of the RLG. It can also be efficiently implemented with hardware and/or software.
One embodiment of the invention is a path length control system which includes a dither pick-off terminal or connection for receiving a dither pick-off signal, a laser intensity monitor (LIM) terminal or connection for receiving a LIM signal that includes single beam signal (SBS) components, and a demodulator clock terminal or connection for receiving a demodulator clock signal. The path length control system also includes a demodulator, an integrator and a blanking controller. The demodulator, which is coupled to the LIM terminal and responsive to a demodulator control signal, provides a demodulated LIM signal to the integrator. The integrator processes the demodulated LIM signal to produce a mirror drive signal. The blanking controller is coupled to the dither pick-off terminal and the demodulator clock terminal. The blanking controller generates the demodulator control gating signals as a function of the dither pick-off signal and the demodulator clock signal. The demodulator control signal causes the SBS components of the LIM signal to be removed from the demodulated LIM signal. In another embodiment the blanking controller includes a blanking pulse generator for producing blanking pulses synchronized in time with the SBS components as a function of the dither pick-off signal.